1. Field of the Invention
The present invention relates to an image inputting device for an endoscope which is capable of providing effective information from overall wavelength regions.
In the known type of endoscope for providing color images which utilizes the field sequential color television method, the light of three primary colors such as red, green and blue is sequentially irradiated onto an object such as an organism, and the reflected light of individual colors is received by an imaging device such as a CCD where it is converted into an electrical signal. After the thus-obtained picture signals are stored in memories in succession, they are converted into color television signals by a processor to be displayed on a color monitor. This type of color endoscope utilizing the field sequential method was proposed, for example, in the specification of U.S. Pat. No. Re. 31290.
Image inputting devices of a type that can be used in the above-described color endoscopes were proposed, for example, in the specification of Japanese Patent Application No. 61-207432. This image inputting device has a structure of the type shown in FIG. 1. More specifically, the image inputting device is made up of: a CCD 101 for providing images of the observed part of an organism, the CCD 101 being located at the end of an inserted section of the endoscope; an amplifier 102 for amplifying the output signal of the CCD 101; a gamma correcting section 103; an analog/digital converter 104; a switch-over switch 105; image memories 106, 107, and 108 connected to the output of the switch-over switch 105 for storing red, green, and blue color picture signals; digital/analog converters 109, 110, and 111 respectively connected to the image memories 106, 107, and 108; and a control signal generating section 112 respectively connected to the analog/digital converter 104, the switch-over switch 105, the image memories for red, green, and blue color picture signals 106, 107, and 108, the digital/analog converters 109, 110, and 111, a synchronizing signal generating circuit 113, and a motor 115 for driving red, green, and blue rotary filters 114. Light from a lamp 116 serving as a light source is irradiated onto the end surface of a light guide 117 through the filters 114, and is led to the forward end of the inserted section of the endoscope through the light guide 117 for illuminating the observed part utilizing the field sequential color television method.
In the thus-arranged image inputting device for an endoscope, the light illuminated from the lamp 116 is decomposed into the three primary colors of red, green, and blue by the rotary filters 114, and the light of these three primary colors is sequentially made incident upon the light guide 117 to irradiate the organism. Visual image information on the organism is converted by the CCD 101 into electrical signals, and these picture signals are input to the amplifier 102 where they are amplified to a predetermined voltage level. The amplified picture signals then enter the gamma correcting section 103 where they are gamma corrected. After the gamma corrected picture signals have been converted into digital signals by the analog/digital converter 104, they enter the switch-over switch 105, and are then sequentially recorded in the red, green, and blue image memories 106, 107, and 108, being changed over by the switch-over switch 105 which is driven by control signals. The picture signals contained in the red, green, and blue image memories 106, 107, and 108 are sequentially read out by the control signals from the control signal generating section 112, and are converted into analog signals by the corresponding digital/analog converters 109, 110, and 111. Thereafter, the analog picture signals are fed out to red, green, and blue picture signal output terminals together with the synchronizing signals from the synchronizing signal generating circuit 113. The thus-obtained red, green, and blue picture signals are presented to a TV monitor for observation of the image provided by the endoscope.
In the above-described image inputting device for an endoscope, a common gamma correcting section is adopted for the red, green, and blue color signals, and these signals are therefore gamma corrected using a non-adjustable output-input characteristic.
However, when the three primary color signals are gamma corrected using a common output-input characteristic in the above-described manner, reproduction of the image obtained by the endoscope is caused to deteriorate in the manner described below: generally, the luminance level of the red component of the object observed by the endoscope is high, and that of the blue component is low, as shown in FIG. 2. Therefore, in gray histograms of the luminance levels of the range shown in FIG. 2 in which the luminance levels are respectively digitized (in an 8-bit, for example) for the red, green and blue colors, the gray levels of the red and blue colors deviate, as shown in FIGS. 3A, 3B, and 3C.
This means that if the red, green, and blue color signals are gamma corrected with the same gamma correcting section by employing the same output-input characteristic, any deviations that take place in the luminance levels of the colors of the object appear in the output color signals. In this case, as shown in FIG. 3A, the red color signal is shifted toward a high level, and is therefore susceptible to saturation. On the other hand, the blue color signal is shifted toward a low level, and is therefore susceptible to being buried in noise, as shown in FIG. 3C.
In such an image reproducing state, since the gray histograms of the primary color signals which are obtained after they have been gamma corrected do not match the luminance levels of the primary colors of the object, the amount of effective information associated with the original image is decreased. Further, since the red color signal deviates toward the high level, signals having a very low level are masked, making discrimination of them difficult.